Use handleChainEnd (#75)

.changeset/shy-guests-heal.md

@@ -0,0 +1,5 @@
+---
+"ai": patch
+---
+
+- Switches `LangChainStream` helper callback `handler` to return use `handleChainEnd` instead of `handleLLMEnd` so as to work with sequential chains

docs/pages/docs/api-reference/langchain-stream.mdx

@@ -26,7 +26,7 @@ The `AIStreamCallbacks` object has the following properties:
 The `LangChainCallbacks` object has the following properties which are compatible with [LangChain's `BaseCallbackHandlerMethodsClass`](https://js.langchain.com/docs)
 
 - `handleLLMNewToken: (token: string) => Promise<void>`: A function that is called for each new token generated by the language model. The token is passed as a parameter.
-- `handleLLMEnd: () => Promise<void>`: A function that is called when the LangChain process is complete.
+- `handleChainEnd: () => Promise<void>`: A function that is called when the LangChain process is complete.
 - `handleLLMError: (e: any) => Promise<void>`: A function that is called when there is an error in the LangChain process. The error is passed as a parameter.
 
 ## Example

docs/pages/docs/guides/langchain.mdx

@@ -45,7 +45,7 @@ export async function POST(req: Request) {
 
 The `handlers` object returned by `LangChainStream` is used to handle certain
 [callbacks](https://js.langchain.com/docs/api/callbacks/) provided by LangChain on your behalf.
-Under the hood it is a wrapper over LangChain's [`handleLLMEnd`](https://js.langchain.com/docs/api/callbacks/classes/BaseCallbackHandler#handlellmend), [`handleLLMNewToken`](https://js.langchain.com/docs/api/callbacks/classes/BaseCallbackHandler#handlellmnewtoken), and [`handleLLMError`](https://js.langchain.com/docs/api/callbacks/classes/BaseCallbackHandler#handlellmerror).
+Under the hood it is a wrapper over LangChain's [`handleChainEnd`](https://js.langchain.com/docs/api/callbacks/classes/BaseCallbackHandler#handlechainend), [`handleLLMNewToken`](https://js.langchain.com/docs/api/callbacks/classes/BaseCallbackHandler#handlellmnewtoken), and [`handleLLMError`](https://js.langchain.com/docs/api/callbacks/classes/BaseCallbackHandler#handlellmerror).
 We wrap over these methods to provide which then write to the `stream` which can then be passed directly to [`StreamingTextResponse`](../api-reference/streaming-text-response#streamingtextresponse).
 
 The result is that ther Vercel AI SDK's [`useChat`](../api-reference/use-chat) and [`useCompletion`](../api-reference/use-completion) work flawlessly:

packages/core/streams/langchain-stream.ts

@@ -10,7 +10,7 @@ export function LangChainStream(callbacks?: AIStreamCallbacks) {
         await writer.ready
         await writer.write(token)
       },
-      handleLLMEnd: async () => {
+      handleChainEnd: async () => {
         await writer.ready
         await writer.close()
       },